Lewis-like structure

Following the obvious parallels with p-block hybridization and bonding, the formation of a duodectet-rule-conforming Lewis-like structural formula for an idealized ML transition-metal complex5 can be pictured as occurring in several steps. 

As an example of a late transition metal, let us consider platinum (k = 8), for which the only Lewis-like structure with monovalent ligands corresponds to... 

According to (4.9c), the number of lone pairs (nfp) in any duodectet-conforming Lewis-like structure is... 

Finally, the favored coordination number (tics = ) of Lewis-like structures must satisfy (4.9a),... 

Let us now specialize to the case of pure sd hybridization, which underlies the duodectet-rule-conforming Lewis-like structures described in Sections 4.2.2 and 4.2.3. Lor equivalent sdM hybrids, Eq. (4.27) becomes... 

Let us first consider metal-metal bonding26 in simple dinuclear hydrides H MMH . For M = Re, for example, the four possible duodectet-rule-conforming Lewis-like structures are... 

Table 4.15. Calculated metal metal (Rmm) and average metal hydride (Rmh) bond lengths, NBO Lewis-like structures, and percentage accuracies of the localized description (%p J for saturated H MMH hydrides (M = Ta-Pt)...

Table 4.15 summarizes optimized bond lengths and NBO Lewis-like structures for 15 saturated normal-valent H MMH compounds (M = W-Pt) as well as corresponding hydrides of hypovalent Ta for comparison. The accuracy of the localized Lewis-like description (as measured by %pf) is found to be reasonably high both for normal-valent and for hypovalent species, typically >98% of the valence-shell density and >99.5% of the total density. 

As in main-group chemistry, hypovalent hydrides of the transition series have pronounced tendencies to form bridging tau bonds. In addition to H4TaTaH4, the multiply bonded species HTaTaH features two symmetrically bridging hydrides. Despite the complexity introduced by such tau bonds, the Ta-Ta interaction clearly has high bond order, as simple Lewis-like structures prescribe. 

Solution The electron count is 16e (eight from Ru, two from each phosphine, one from each Cl, and two from methylene, assumed to make a Ru=C double bond). Two cu bonds result, leaving four electrons to make the ctruc and 7TruC bonds and two lone pairs. Skeletal sigma-bonding of the parent Lewis-like structure requires three sd2 hybrids (90° angles),... 

A still more dramatic example is given by the saturated decahydride of ditungsten, H5WWH5, which has the formal Lewis-like structure... 

Objective 8 We can draw a Lewis-like structure that provides a better description of the actual... 

LEWIS-LIKE STRUCTURES IN TRANSITION METAL BONDING... 

Lewis-Like Structures in Transition Metal Bonding 87 ----------f/0 4,16---------------------------------... 

As a simple illustration of transition metal hybridization and Lewis-like structures, let us consider tungsten hexahydride (WHg) as a prototype of idealized sd hybridized bonding. The input file and chosen atomic numbering for the optimized (B3LYP/LANL2DZ-level) geometry of WHs are given in FO-4.16. 

---